Horseshoeing Part 1

A Text-Book of Horseshoeing

by A. Lungwitz and John W. Adams, copyright 1897

This is the first part in what will be a complete reprint of Lungwitz & Adams’ important ‘Textbook of Horse-Shoeing’ originally written in the 1880’s and containing some remarkably modern information. This volume goes into the greatest detail on the subject and with a intelligent clarity that belies how old it is. Coming as it did at end of the first horse era, and well before anyone might have reasonably predicted the advent of the automobile and tractor, it is apparent how important the equine was to the whole of society. The authors, of Germany and Pennsylvania, compiled what was, at the time, to be the ultimate word on the subject. As with all of the reprints we have offered over forty years time, we trust that readers will be triggered by these words to complete their education with diligence and introspection. Just because something is old doesn’t always make it right, and of course just because something is new doesn’t make it the true culmination. LRM

INTRODUCTION

HORSESHOEING is an industry which requires, in equal degree, knowledge and skill. The word “horseshoeing” embraces various acts, especially preparing the iron sole, the horseshoe; forming it and fitting it to the hoof, whose ground-surface has been previously dressed in accordance with the direction of the limb, and fastening it to the hoof by means of nails.

Owing to the complicated structure of the hoof, success in the practice of horseshoeing requires a knowledge of the anatomy and physiology of the horse’s body in general and of the foot in particular.

The object of shoeing is, —

1. To protect the hoof from excessive wear, and thus render the horse continuously serviceable upon our hard roads.
2. To prevent slipping and falling during the winter season.
3. To so far remove the disadvantages of faulty positions of the limbs that horses may render good service, and, in some cases,
4. To cure or improve diseased or defective hoofs or feet.

Horseshoeing, though apparently simple, involves many difficulties, owing to the fact that the hoof is not an unchanging body, but varies much with respect to form, growth, quality, and elasticity. Furthermore, there are such great differences in the character of ground-surfaces and in the nature of horses’ work that shoeing which is not performed with great ability and care induces disease and makes horses lame.

In view of these facts, a thorough training of the young horseshoer in the principles and practice of his trade is not only greatly to be desired, but is really essential to success; unreasoning work does as much harm in this as in any other vocation. A good common-school education is necessary (more will do no harm). Further requisites are a healthy body, not too tall, liking for the work, aptness, an active, reasoning mind, fearlessness, dexterity, a good eye for proportion, and, finally, careful selection of a master-instructor. Theoretically educated, practically experienced and approved masters, in whose shops all kinds of horses are shod, are to be preferred.

During his term of apprenticeship the young apprentice should learn to make drawings of horseshoes, of tools of the trade, and of hoofs of various forms, and should also make one or more model shoes as an indication of his ability. After completing his time he should seek a position in a first-class shop, either at home or abroad. A visit to foreign lands will widen one’s mental horizon and make him a broader, abler man in every respect. Later, opportunity will be given to some (in Germany) to join the cavalry, and thus acquire a good education in shoeing under the patronage of the government. Finally, a course of instruction in a school of horseshoeing will convert an already practical and intelligent horseshoer into a thoughtful, capable, expert workman.

The scope of horseshoeing is by no means so narrow and insignificant as it may appear, and since a knowledge of anatomy and physiology of the horse’s body in general, and of the foot in particular, is necessary, it is evident that the schools of horseshoeing in which one can get the best instruction are those in which there is not only a regularly graded course of instruction, with demonstrations upon dissected material and upon living horses, but also an abundance of daily work at the forge and on the floor in the shoeing of horses. A course of four to six weeks is not sufficient.

Furthermore, it should be borne in mind that schools of horseshoeing are not for the purpose of instructing young men in all matters which pertain to the trade, but only in the making of shoes, the critical examination and management of hoofs, and the rational and skilful performance of shoeing. For this reason it is not advisable for young men to attend a school of horseshoeing until they have at least completed their apprenticeship.

PART 1 CHAPTER 1

THE GROSS ANATOMY OF THE HORSE

The supporting structure of the horse’s body is the bony framework or skeleton (Fig. 1). We distinguish in the skeleton the bones of the head, trunk, and limbs.

The bones of the head are numerous and, excepting the lower jaw, are solidly united with one another. In general, we distinguish in the head only the upper and lower jaws (1 and 1′). Both form various cavities; for example, the cranial cavity, in which the brain lies, the orbital cavities (eye-sockets), the nasal passages, and the mouth. Besides, the teeth are set in the jaws.

The trunk comprises the bones of the spinal column, thorax, and pelvis.

The spinal or vertebral column (2 to 6), which bears the head at its anterior end, is the chief support of the entire skeleton. It consists of from fifty-two to fifty-four single and irregular bones called vertebrae, placed in the upper part of the median vertical plane of the body. Each vertebra, which the exception of those of the tail (coccygeal or caudal vertebrae), is traversed by a large opening called the vertebral foramen. The vertebrae are placed end to end in a row, and through them runs a continuous large canal called the vertebral or spinal canal, in which lies the spinal cord. The horse has seven cervical, eighteen dorsal, six lumbar, five sacral, and sixteen to eighteen caudal vertebrae. The sacral vertebrae are grown together to form one piece called the sacrum.

The thorax is formed by the ribs and the breast-bone or sternum. The horse has eighteen ribs on each side (7), and all articulate with the dorsal vertebrae. The first eight pairs unite by their lower ends directly to the sternum or breast-bone, and are therefore called true ribs, while the last ten pairs are only indirectly attached to the sternum, and are consequently called false ribs. The sternum (8) lies between the forelegs, and helps to form the floor of the chest cavity. The space enclosed by the bones of the thorax is called the thoracic, pulmonary, or chest cavity, and contains the heart and lungs. The bones of the pelvis form a complete circle or girdle. The upper part, called the ilium (9′), articulates on its inner side with the sacrum (5), while its outer is prolonged to form a prominent angle, which is the support of the hip, and is called the “point of the hip.” The posterior part of the pelvis is called the ischium (9”), and that part lying between the ilium and the ischium and forming part of the floor of the pelvis is called the pubis.

The space between the thorax and the pelvis, bounded above by the lumbar vertebrae and shut in below and on the sides by the skin and muscular walls of the belly (abdomen), is called the abdominal cavity. This cavity opens directly into the pelvic cavity, and contains the stomach, intestines, liver, spleen, pancreas, kidneys, and a part of the generative organs. The thoracic and abdominal cavities are separated by a muscular partition, the diaphragm.

The bones of the limbs may be likened to columns, upon which the body rests; they articulate with one another at various angles, are tubular in structure, and strong.

The bones of the fore-limbs do not articulate directly with the bones of the trunk, but are attached to the body by means of the skin and muscles. From above to below we distinguish the following bones:

1. The scapula, or shoulder-blade (10), a flat, triangular bone, prolonged at its upper border by a flat, very elastic cartilage, called the scapular cartilage. At its lower end the scapula articulates with —
2. The upper end of the humerus (11), forming the shoulder-joint (scapulo-humeral articulation). The humerus articulates at its lower end with —
3. The radius (12) and the ulna (13), to form the elbow-joint. These two bones are the basis of the forearm. The ulna, smaller and weaker than the radius, lies behind and projects above it to form the point of the elbow. The lower end of the radius articulates with —
4. The carpus, or knee (14), which comprises seven small, cubical bones disposed in two horizontal rows, one above the other. The upper row comprises four bones and the lower row three. The lower row rests upon —
5. The large metacarpal or cannon bone, and the two rudimentary metacarpal or splint-bones. The lower end of the radius, the upper ends of the metacarpal bones, and the small carpal bones together form the carpal or the knee-joint (wrist of man). Of the metacarpals, the middle one is the largest, longest, strongest, and most important, and is called the large metacarpal, cannon, or shin-bone (15). It articulates at its lower end with the os suffraginis, or long pastern (17), and with the two small sesamoid bones (20). On each side of the upper part of its posterior surface like the two long, slender split-bones (16). The inner splint-bone is sometimes affected with bony thickenings (exostoses) called “splints.”
6. The bones of the phalanges (all bones below the cannon) will be fully described in another place.

The bones of the hind limbs articulate directly with the pelvis at the hip-joint. They are stronger than the bones of the anterior limbs. We distinguish the following bones in the hind legs:

1. The highest bone in the hind limb is the femur (21). It is the strongest bone in the entire body. It lies in an oblique direction downward and forward, and at is lower end articulates with —
2. The patella (22), the tibia (23), and the fibula (24), to form the stifle-joint (knee of man). The patella plays over the anterior surface of the lower end of the femur. The fibula is small, and lies against the upper and outer side of the tibia. The latter at its lower end articulates with —
3. The bones of the tarsus, or hock (25), which are six small, irregular bones disposed in three rows, one above another. The os calcis, or heel-bone, and the astragalus are in the upper-most row, and are the most important. The former projects above the true hock-joint from behind, to form a long lever, the upper end of which is called the “point of the hock,” and the latter articulates with the tibia. The tarsal (hock) bones articulate below with-
4. The metatarsal bones (26 and 27), which are longer, and the cannon narrower from side to side, than the corresponding metacarpal bones, but are otherwise similar.
5. The phalanges of a hind limb (28 to 31) are also narrower than those of a forelimb, but are nearly alike in other respects.

All the horse’s bones present small, but more or less distinct openings (nutrient foramina) for the passage of blood-vessels and nerves. Many bones possess roughened elevations and depressions, to which ligaments, tendons, or muscles are attached. With the exception of the os pedis, all bones are enveloped in a sort of “bone-skin” called periosteum. The bones unite among themselves to form either movable or immovable unions. A movable union between two or more bones is termed a “joint,” or articulation. The articulating ends of the bones, presenting on one side a convex surface (head or condyle) and on the other a corresponding concave surface (glenoid or cotyloid cavity) are covered with elastic articular cartilage. The bones are bound together by means of ligaments, which are tough, fibrous, cord-like, or sheet-like structures. Ligaments are either (1) capsular or (2) funicular (cord-like). Every articulation in the limbs possesses a capsular ligament, and all, except the shoulder-joint, have several funicular (cord-like) ligaments. The capsular ligaments are lined upon their inner face with a delicate membrane (synovial membrane) which secretes the synovia, or “joint water,” whose function is to lubricate the joint and prevent friction; they enclose the joint in a sort of air-tight cuff or sack. The funicular ligaments are very strong and often large, and are the chief means of union of the bones. The immovable articulations are termed sutures; they are found principally in the head. The mixed joints are found between the bodies of the vertebrae, each two of which are united by an elastic fibro-cartilage which, in the form of a pad, lies between them, and by its elasticity allows of very slight movement, though the spinal column as a whole can execute manifold and wide movements, as shown by the neck and tail.

Joints which permit motion in all directions are known as free joints; such are the shoulder- and hip-joints (ball-and-socket joints). Those which admit of motion in but two directions (flexion and extension), and often to a very limited extent, are called hinge-joints – e.g., the elbow, hock, and fetlock. The joints between the long and short pasterns and between the letter and the pedal bone are imperfect hinge-joints, because they allow of some other movements besides flexion and extension. The articulation between the first and second cervical vertebrae (atlas and axis) is called a pivot-joint.

The skeleton represents a framework, which closely approaches the external form of the body, and by reason if its harness and stiffness furnishes a firm foundation for all other parts of the body. By reason of the great variety of position and direction of the bones, and of the fact that changes of position of each single part of this complicated system of levers may result in the greatest variety of bodily movements, we can easily understand how the horse is enabled to move from place to place. Of course, the bones have no power of themselves to move, but this power is possessed by other organs that are attached to the bones. These organs are the muscles, and, owing to their ability to contract and shorten themselves, and afterwards to relax and allow themselves to be stretched out, they furnish the motive power that is communicated to and moves the bones.

The muscles of the body massed together are the red flesh which we observe in every slaughtered animal. They are not, however, so shapeless as they appear while in this condition; on the contrary, they present well-arranged muscular layers of variable size, thickness, length, and position. (See Fig. 2.) The muscles clothe the skeleton externally, give the body its peculiar form, and, by their special power of contraction, change the relative positions of the bones and thus make it possible for the animal to move. For this reason, the muscles are called the active, and the bones the passive, organs of motion. By carefully examining a muscle it will be found to consist of actual, minute, reddish, muscular fibres. As a rule, muscles terminate in more or less strong, glistening, fibrous cords called tendons, or fibrous sheets termed aponeuroses, by which they are attached to the bones. In the limbs are muscles terminating in very long tendons, which act as draw-lines upon the distant bones of the foot (long and short pasterns and pedal bone) and set them in motion. Such long tendons are enclosed in sheaths of thin, membranous tissue, known as tendon sheaths. The inner surface of such a sheath is in direct contact with the surface of the tendon, and secretes a thin slippery fluid (synovia) which lubricates the tendon and facilitates its gliding within the sheath.

As long as the bones, articulations, muscles, and tendons of the limbs remain healthy, just so long will the legs maintain their natural direction and position. Frequently, however, this normal condition of the limbs is gradually altered by disease of the bones, joints, and tendons, and defects in the form and action of the lower parts of the limbs arise that often require attention in shoeing.

THE FOOT

A. The Bones of the Foot

Since the horse is useful to man only by reason of his movements, his foot deserves the most careful attention. The horse-shoer should be familiar with all its parts. Fig. 3 shows the osseous framework of the foot, consisting of the lower end of the cannon bone (A), the long pastern (B), the two sesamoid bones (C), the short pastern (D), and the pedal bone (E). The lower end of the cannon, or large metacarpal bone (A) exhibits two convex articular surfaces (condyles) separated by a median ridge running from before to behind, and all covered by articular cartilage. On both the external and internal aspects of the lower end of the cannon are small uneven depressions in which ligaments take their attachment.

The condyles of the cannon articulate with the os suffraginis (long pastern) and the two sesamoids (Figs. 3, C, and 4, B) in such a manner that in the forefeet the cannon makes an angle with the long pastern of from one hundred and thirty-five to one hundred and forty degrees, and in the hind feet of from one hundred and forty to one hundred and forty-five degrees.

The long pastern (first phalanx) (Fig. 4, A) is about one-third the length of the cannon; its upper and thicker end presents two condyloid cavities (a) (glenoid cavities), separated by a median groove, which exactly fit the condyles and ridge at the lower end of the cannon. The lower end of the long pastern is smaller than the upper, and is provided with two condyles, between which is a shallow groove (e). The anterior face of the bone is smooth, rounded from side to side, and blends into the lateral borders. The posterior face is flatter, and shows a clearly marked triangle to which ligaments attach.

The two sesamoid bones (Fig. 4, B) are small, and somewhat pyramidal in shape, and, lying against the posterior part of the condyles of the cannon bone, increase the articular surfaces at the upper end of the long pastern.

The short pastern (second phalanx) (Figs. 5 and 6) lies under the first phalanx and above the os pedis; it is somewhat cubical in shape. Its upper articular surface (Fig. 5, a) presents two glenoid cavities to correspond with the condyles of the first phalanx. The lower articular surface (Fig. 5, d) resembles the lower end of the first phalanx. The upper posterior border of this bone is prominent and prolonged transversely (Fig. 6, a), to serve as a supporting ledge for the first phalanx, as a point of attachment for the perforatus tendon, and as a gliding surface for the perforans tendon.

The lowest bone of the limb is the third phalanx or os pedis (Fig. 7). In form it is similar to the hoof. The anterior or wall-surface (a) is rough, like pumice stone. Above and in front is the pyramidal eminence to which the tendon of the anterior extensor of the phalanges attaches. Behind, the bone extends backward to form the inner and outer branches (c, c) or wings of the os pedis. The upper, articular surface (b) slopes backward and downward. The lower, solar or plantar surface (Fig. 8, a) is slightly concave, and presents posteriorly a half-moon-shaped excavation, with a roughened border called the semilunar crest (c), to which the perforans tendon attaches; just above this crest are two small holes (e) known as the plantar foramina, through which the plantar arteries pass into the bone. The surfaces of wall and sole come together in a sharp edge, which is circular in its course. It is easy to tell whether a pedal bone is from a fore or a hind limb; the os pedis of a hind leg has a steeper and more pointed toe, and a more strongly concaved solar surface than the same bone of a foreleg. Not only is the outline of the sharp inferior border of the os pedis of a front foot more rounded at the toe, but when placed on a flat surface the toe does not touch by reason of being turned slightly upward, much as a shoe designed to give a “rolling motion.” The os pedis of a hind foot is narrower from side to side (pointed), and does not turn up at the toe.

The right and left hoof-bones are also, as a rule, easily distinguished by variations in the surfaces of wall and sole. The shape of the os pedis corresponds to the form of the horny box or hoof, and therefore a knowledge of this bone is absolutely necessary.

The navicular bone (os naviculare, nut-bone, Fig. 9 and 10) is an accessory or sesamoid bone to the os pedis. It is a small bone, transversely elongated and situated behind and below the os pedis and between the wings of the latter. It adds to the articular surface of the pedal joint. Its under surface is smooth, and acts as a gliding surface for the perforans tendon which is quite wide at this point.

The long axes of the three phalanges (os suffraginis, os coronae, and os pedis) should unite to form a straight line, when viewed either from in front or from one side; that is, the direction of each of these three bones should be the same as the common direction of the three considered as a whole.

B. The Articulations of the Foot.

There are three articulations in the foot – namely, the fetlock, coronary, and pedal joints. All are hinge-joints, the fetlock being a perfect hinge-joint, and the other two imperfect hinge-joints. Each has a capsular ligament, and also several funicular or cord-like ligaments which are placed at the sides of (lateral ligaments), or behind (on the side of flexion) the joint.

I. The fetlock or metacarpo-phalangeal articulation is formed by the condyles at the lower end of the cannon bone and the glenoid cavities formed by the union of the articular surfaces of the sesamoids and the upper end of the first phalanx. The following ligaments are about this joints:

1. Two lateral ligaments, an external and internal (Fig. 11, a).
2. Two lateral sesamoid ligaments (f).
3. An intersesamoid ligament (Fig. 12, b), a thick, fibrous mass, binding the sesamoid bones almost immovably together, extending above them and presenting on its posterior face a smooth groove, in which glide the flexor tendons of the phalanges (perforans and perforatus).
4. The suspensory ligament of the fetlock (Figs. 11, c, 12, c, and 13, c). This may also be called the superior sesamoid ligament. It is a long and very powerful brace, originating on the lower row of carpal bones (bones of the hock in the hind leg) and on the upper end of the cannon between the heads of the two splint-bones, and dividing at the lower third of the cannon into two branches (c), which are attached one to each sesamoid bone. Below these bones these two branches are prolonged obliquely downward and forward on opposte sides of the lond pastern to pass into the borders of the anterior extensor tendon of the toe at about the middle of the long pastern (Fig. 14, b’).
5. The inferior sesamoid ligament (Figs. 11, d’, 12, d, d’, and 13, d’ and E). This originates at the lowest part of the sesamoid bones and intersesamoid ligament and consists of three parts or branches. The median branch (d) is the longest and strongest, and takes its lower attachment in the middle of the fibro-cartilaginous lip found on the upper border of the posterior face of the second phalanx. The two lateral branches (d’) approach each other as they descend, and terminate on the sides of the roughened triangle on the posterior face of the first phalanx.
6. The deep inferior sesamoid ligament (Fig. 13, e) is quite short, and consists of a number of distinct, thin fibrous bands lying directly against the bone and entirely covered by the median and lateral inferior sesamoid ligaments. These fibrous bands cross one another in passing from the sesamoids to the first phalanx.

II. The coronary joint is the simplest of the three articulations of the foot. The long pastern furnishes two condyles and the short pastern two glenoid cavities. Besides a capsular ligament there are —

1. Two lateral coronary ligaments (k), and,
2. Six posterior coronary ligaments, — namely, two superior coronary ligaments (h), two median coronary ligaments (h’), and two inferior coronary ligaments (g).

III. The pedal articulation (“coffin” joint) is an imperfect hinge-joint, and is formed by the condyles at the lower end of the short pastern and the two glenoid cavities in the united upper surfaces of the pedal and navicular bones. Besides the capsular ligament (Figs. 12 and 13, l), which binds all three bones together, there are the following accessory ligaments:

1. Two strong lateral ligaments, an external and an internal (Fig. 11, i), whose posterior borders are lost in the lateral cartilages which cover them.
2. Two lateral suspensory ligaments of the navicular bone (k). They begin on the posterior border and ends of the navicular bone, and terminate on the lower part of the anterior surface of the os suffraginis, where they are lost in the lateral ligaments of the coronary articulation.
3. The lateral ligaments of the lateral cartilages, navicular bone, and os pedis. They are short, and unite the navicular bone with the os pedis and lateral cartilages.

Of the three phalangeal articulations, the pedal is the only one that permits of any lateral movement; hence it is an imperfect hinge-joint.

C. The Locomotory Organs of the Foot.

Though the muscles are the organs which produce motion, the horseshoer need concern himself only with the tendons of those muscles which extend and flex the phalanges. These tendons are either extensors or flexors. The extensors lie on the anterior face and the flexors on the posterior face of the phalanges.

The anterior extensor of the phalanges (Fig. 14, a) extends the long and short pasterns and the hoof-bone; it is broad, and made somewhat broader by receiving the branches of the suspensory ligament (b’) that some from the sesamoid bones. It takes a firm attachment on the pyramidal eminence of the os pedis. In the forefeet the long pastern has a special extensor tendon (c), which is known as the lateral extensor. When the muscles to which these tendons are attached act – that is, when they draw themselves together, or contract as we term this action – the foot is carried forward (extended).

There are two flexor tendons of the phalanges – namely, the superficial (perforatus tendon) and the deep (perforans tendon).

1. The superficial flexor or perforatus tendon (Figs. 15, b, and 16, a, b) lies behind, immediately under the skin, and covers the deep flexor or perforans tendon. At the gliding surface between sesamoid bones (Fig. 15, b’) through which the perforans tendon (a”’) passes, while a short distance farther down it bifurcates, or divides into to branches (Figs. 15, b”, and 16, b), which terminate, one on either side, partly on the inferior lateral borders of the first phalanx and partly on the fibro-cartilage of the second phalanx. It acts simultaneously on the long and short pasterns.
2. The deep flexor or perforans tendon (Figs. 15, a, and 16, c) is cylindrical and stronger than the perforatus tendon; above the fetlock-joint it lies between the perforatus and the suspensory ligament of the fetlock. At the sesamoid bones it passes through the ring formed by the perforatus tendon (Fig. 15, b’), then becomes broad and double-edged, passes between the two terminal branches of the perforatus, glides over the fibro-cartilage of the second phalanx and over the inferior surface of the navicular bone, and finally ends on the semilunar crest of the third phalanx. In common with the perforatus tendon it flexes the foot.

If a point a few inches above the fetlock a limb be cut through from behind, the knife will pass successively through the following structures; skin, perforatus tendon, perforans tendon, suspensory ligament, cannon bone, lateral extensor tendon, anterior extensor tendon, and lastly, the skin on the anterior surface of the limb. The flexor tendons are frequently thickened and shortened by inflammation due to injury, and as a result the foot is pulled backward and the hoof grandually becomes nearly upright – i.e., stubby, steep-toed. A knowledge of the normal condition of the tendons is, therefore, absolutely necessary to the horseshoer. Both flexor tendons are embraced and held in place by ligaments and fascia passing our from the phalanges (Figs. 16, d’, and 24, e, f). The extensor and flexor tendons essentially contribute to the strong union of the phalangeal bones, and especially to the support and stability of the fetlock-joint. The gliding of the tendons is made easy by the secretion of a lubricating fluid, called synovia, from the inner surface of the sheaths which surround them. In thin-skinned well-bred horses with sound limbs, one can not only distinctly feel the tendons through the skin, but can see their outline. When the tendons and bones are free from all inflammatory thickenings, and the tendon sheaths are not visibly distended, we say that the leg is “clean.”

Mucous Bursae and Tendon Sheaths.

Accessory to the tendons, there are in the foot roundish, membranous sacs (mucous bursae) and membranous tubes (tendon sheaths). Both contain a liquid resembling synovia (“joint water”), which facilitates the gliding of the tendons. These bursae and sheaths are often distended to form soft tumors, known as hygromata (“wind-puffs,” “wind-galls”).

(a) Mucous Bursae. – They lie beneath tendons at those places where the tendons pass over bony prominences.

1. The mucous bursa of the anterior extensor tendon of the toe is about the size of a walnut, and lies between the tendon and the capsular ligament of the fetlock-joint (Figs. 17, g, and 18, e).
2. The mucous bursa of the extensor tendon of the long pastern (lateral extensor) is somewhat smaller, and lies, likewise, beneath the tendon, between it and the capsular ligament of the fetlock-joint (Fig. 17, h).
3. The mucous bursa of the navicular region lies between the under surface (gliding surface) of the navicular bone and the flexor pedis perforans tendon (deep flexor). Its width equals the length of the navicular bone, and it extends upward and downward beyond the bone. Above, it is separated from the sheath of the perforans tendon (“great sesamoid sheath”) by a membranous partition; below, it passes to the attachment of the perforans tendon to the semilunar crest of the os pedis.

(b) There is but one tendon sheath in the foot – the sheath common to the two flexor tendons (great sesamoid sheath). It encloses the flexor tendons from the middle third of the cannon down to the middle of the short pastern, and is intimately united with the flexor pedis perforans tendon (Fig. 17, f, f’, f”, f”’. Fig. 18, d, d’, d”, d”’).

Alerting the Relative Tension of the Flexor Tendons and Suspensory Ligament of the Fetlock-Joint.

The body-weight imposed at the fetlock-joint is supported, in large part, by the suspensory ligament; somewhat less weight is borne by the perforans tendon, and a still smaller amount by the perforatus. The coronary joint is supported chiefly by the perforatus, assisted by the perforans. The pedal joint is pressed forward and upward by the perforans tendon passing in a curve beneath the navicular bone. Each of these three structures bears its normal proportion of the body-weight when the three phalanges, as viewed from the side, form a continuous straight line from the fetlock-joint to the ground. In such a case the obliquity of the long foot pastern will be the same as that of the toe (see Foot-Axis, p. 70.)

Raising the toe by means of a tip, a full shoe with thinned branches or a toe-calk, or pairing away the quarters will tilt the os pedis backward, break the foot-axis backward in the pedal joint and to a less extent in the coronary joint, and increase the tension of the perforans tendon considerable and of the perforatus slightly. These tendons tightening behind the fetlock-joint force it forward, causing the long pastern to stand steeper, and taking some strain from the suspensory ligament. Hence, the perforans tendon is under greatest tension, and the suspensory ligament under least tension, when the foot-axis is broken strongly backward.

Shortening the toe, or raising the quarters by heel-calks or thickened branches, will tilt the os pedis forward, break the foot-axis forward in the pedal joint, and will greatly lessen the tension of the perforans tendon. The aggregate tension of perforans and perforatus tendons being diminished, the fetlock sinks downward and backward, the long pastern assumes a more nearly horizontal direction, and the tension of the suspensory ligament is increased. Thus, the perforans tendon is under least tension, and the suspensory ligament under greatest strain, when the foot axis is broken strongly forward.

D. The Elastic Parts of the Foot.

All bodies which under pressure or traction change their form, but return again to their original shape as soon as the pressure or traction ceases, are called elastic or springy. Nearly all parts of the horse’s foot, except the bones, possess more or less elasticity. The lateral cartilages and the plantar cushion are elastic to a high degree, but the coronary band, the lamince, the articular cartilage, and the horny box or hoof are less elastic. This property of characteristic is possessed by the respective parts of the foot in accordance with their function, location, and structure.

The two lateral cartilages (Figs. 19, C and 20, b) are irregular, quadrangular plates, attached to the wings of the os pedis, and extending so far upward and backward that one can feel them yield to pressure on the skin above the coronet, and can thus test their elasticity. The perforans tendon and the plantar cushion lie between the lateral cartilages, and on the sides and behind are partially enclosed by them. The internal concave surface of the lateral cartilage (Fig. 20) is attached to the plantar cushion, os pedis, the navicular bone, and, like the external, slightly convex surface, is covered with many blood-vessels (veins) (Fig. 25, B).

The plantar cushion (Figs. 21, 22, 23) is composed almost entirely of yellow elastic and white fibrous tissues, with adipose (fat) cells distributed throughout their substance. It is similar in form to the horny frog, and lies between it and the perforans tendon (Fig. 24, a). The bulbs are formed by the posterior thicker portion which lies between the lateral cartilages and is divided into two parts by the cleft or median lacuna (Figs. 21, a, and 23, d). The summit is attached to the plantar face of the os pedis in front of the semilunar crest, and the bulbs are attached to the lateral cartilages. It is covered inferiorly by the velvety tissue of the frog (pododerm).

E. The Blood-Vessels and Nerves.

Vessels which carry blood from the heart to the tissues are called arteries, while those which return the blood to the heart from the tissues are called veins. Arteries and veins are connected by very small, thread-like vessels called capillaries, which originate in the smallest arteries and are so minute that they can not be seen without the aid of a microscope. The capillaries penetrate the soft tissues in every direction, and finally unite to form small veins. For our purpose we need consider only the arteries and veins.

The arteries carrying blood from the heart ramify and subdivide in all parts of the body, and thus reach the foot. They are thick-walled, very elastic tubes, without valves, and carry bright-red blood, which flows in spurts, as can be seen when an artery is cut. If a finger be pressed lightly over an artery lying near the surface, the blood-wave can be felt as a light stroke (pulse). The character of the pulse is important, because in inflammations of the pododerm or horn-producing membrane of the foot we can ascertain by feeling that the pulse is stronger than usual in the large arteries carrying blood to the inflamed foot.

On either side of the phalanges below the fetlock-joint there lies an artery called the digital artery (Fig. 25, a). The pulse can be felt in it as it passes over the fetlock at A, Fig. 25. It gives off the following collateral (side) branches: 1. The artery of the first phalanx (perpendicular artery), with anterior and posterior branches. 2. The artery of the plantar cushion, which supplies with blood the plantar cushion, the velvety tissue of the sole and frog, the bar portion of the coronary band, and the sensitive laminae of the bars. 3. The coronary artery, which carries blood to the coronary band, os coronae, ligaments of the coronary and pedal joints, flexor tendons, and skin.

The terminal branches of the digital arteries are the preplantar and plantar ungual arteries. The preplantar artery passes through the notch in the wing of the os pedis, then along the preplantar fissure, splitting up into many branches, which spread over and penetrate the porous surface of the os pedis. The plantar artery courses along the plantar fissure, enters the plantar foramen, and passes into the semilunar sinus of the os pedis, where it unites with the terminal branch of the opposite digital artery, forming the semi-lunar arch.

After the arterial or pure blood passes through the capillaries it is collected by the veins, to be returned to the heart; then it is driven to the lungs for purification, and is again returned to the heart, from whence it is pumped through the arteries to all parts of the body.

The veins are more numerous than the arteries; they have thinner walls, and the larger ones are provided with valves that prevent the impure blood from flowing backward. The veins carry impure or dark-red blood towards the heart, and if one is opened the dark blood flows in a steady stream; it does not spurt. The great number of veinlets in the lower parts of the foot form a complex net-work (plexus) of vessels which are in such manifold and close union with one another that checking the flood in one part does not seriously interfere with the flowing of the blood towards the larger veins. The following are the most important of these net-works of veins or veinous plexus: (1) the solar venous plexus (Fig. 26, D); (2) the podophyllous venous plexus (Fig. 25, C); (3) superficial coronary venous plexus (Fig. 25, B); (4) bulbar venous plexus (Fig. 26, B). All these plexus of small veins contribute to form the digital veins (Fig. 25 and 26, A).

Nerves are roundish white cords which come from the brain and spinal cord; they generally accompany arteries. They divide and subdivide into smaller and smaller branches till they become invisible to the naked eye and are lost in the tissues. The nerves that are found in the foot come from the spinal cord, and because the largest nerves of the foot accompany the digital arteries they are called digital nerves (Fig. 25, 1). The branches ramify throughout all parts of the foot except the horny box and the hair. Nerves, according to their use or function, are classed as motor and sensory. The motor nerves end in muscles which they stimulate to action and control. The sensory nerves terminate in the skin and in the soft tissues just under the horny box or hoof (pododerm), and render these parts sensitive; that is, they convey certain feelings, as, for example, the pain caused by bruising, pricking, or close-nailing, to the brain and consciousness.

F. The Protective Organs of the Foot

The protective organs are the skin and the horny box or hoof.

The external skin, or hide, covers the entire body; in the feet it covers the bones, tendons, and ligaments, even passing in under the hoof and directly covering the os pedis. This portion of the skin, enclosed by the hoof and therefore invisible, is called the pododerm or foot-skin. In Germany it is called the hoof-skin (huflederhaut), because it is a continuation of the outer visible skin, and because it secretes the hoof – that is, the hoof is produced by it. That part of the skin which is covered with hair is known as the external or hair-skin.

(a) The hair-skin (Fig. 27, a) consists of three superposed layers – (1) the external superficial layer, or epidermis; (2) the middle layer, derm or leather-skin (so-called because leather is made from it); (3) the internal layer, or subcutaneous connective tissue.

1. The external layer, or epidermis, is composed merely of single flattened, horn-like cells (scales) lying side by side and over one another, and uniting to form one entire structure – a thin, horn-like layer, without blood-vessels or nerves. It extends over the entire surface of the body, and protects the underlying, very sensitive middle layer from external influences. The oldest cell-layers lie on the outer surface, and are being continuously brushed off in patches or scales, while new ones are constantly being formed on the outer surface of the middle layer.
2. The middle layer, leather-skin or dermis, is composed of solid, fibrous, and elastic tissues, and contains many blood-vessels, small nerves, sweat- and oil-glands, and hair follicles from which the hair grows. The hair upon the posterior surface of the fetlock-joint is usually long and coarse, forming a tuft known as the “footlock,” which encloses a horny spur, called the ergot. Common bred horses have, as a rule, larger and coarser footlocks than thoroughbreds. The derm or leather-skin, which produces the hair and epiderm, is the thickest and most important layer of the skin.
3. The inner layer, or subcutaneous tissue, unites the middle layer with the muscles, tendons, ligaments, bones, or other structures. It is that loose fibrous mesh or net-work through which the butcher cuts in removing the hide from the carcass.

(b) The hoof-skin (Figs. 27 and 28, b, c, d), or pododerm, is completely enclosed by the hoof. Although it is only an extension of the derm or middle layer of the hair-skin, it differs from the latter in structure and relations.

In order to study the pododerm we should not wrench the hoof off with violence, but should allow the foot to partially decompose by leaving it for six to eight days at ordinary room temperature; it can then be removed without injuring the pododerm. After the hoof has been removed the entire pododerm presents a more or less dark-red color (flesh-color), which is due to the great number of blood-vessels that it contains. For this reason different parts of the pododerm have received the prefix “fleshy,” as for example, fleshy wall, fleshy sole, fleshy frog, etc. The pododerm is what the uninformed horseshoer calls the “quick.” I will here remark that the three layers of the external or hair-skin are represented in the foot; however, the epidermis is in an entirely different form – namely, the horny box or hoof. The internal layer or subcutaneous tissue of the hair-skin is absent in those parts of the foot where the pododerm covers the os pedis. There remains, therefore, only the middle layer, derm, or pododerm, which secretes the hoof, and which is the prolongation and representative of the middle layer of the hair-skin. The pododerm is distinguished from the derm of the hair-skin chiefly by the absence of hairs, oil- and sweat-glands, and the presence on its outer surface of fleshy, sensitive laminae and small thread-like projections called villi.

The pododerm consists of five different parts: the perioplic band, the coronary band, the sensitive laminae (podophyllous tissue), the velvety tissue of the sole, and the velvety tissue of the fleshy frog.

1. The perioplic band (Fig. 28, b) is a narrow ridge, about one-fifth to one-fourth or an inch wide, lying between the hair-skin and the coronary band. Somewhat broader at the toe than on the sides, it broadens out near the bulbs of the heels, over which it passes to end in the velvety tissue of the fleshy frog. It is separated from the coronary band by a narrow depression called the coronary furrow (Moeller). The surface of the perioplic band glistens faintly, and is thickly studded with numerous thread-like projections called villi, which are from one twenty-fourth to one-twelfth of an inch in length. The perioplic band secretes the soft horn of the perioplic ring and the perioplic or varnish-like outer layer of the wall.

2. The coronary band (Fig. 27, c) lies between the perioplic band and the sensitive laminae or fleshy leaves. It presents a prominent convex band or cushion about three-fourths of an inch wide, which extends entirely around the foot from one bulb of the heel to the other. In front it directly covers the anterior extensor tendon of the toe, and at the sides the lateral surfaces of the os coronae and the upper part of the lateral cartilages, while farther back towards the heels the lateral cartilages project considerably above both coronary and perioplic bands. The coronary band is more convex (rounded) in front than on the sides of the foot, and is flattened in the region of the bulbs of the heels. Its surface is thickly covered with villi, which are longer and stronger than those of the perioplic bands. At the bulbs of the heels the coronary band turns forward and inward along the fleshy frog nearly to its summit. This portion of the coronary band is from one-third to one-half an inch wide, and is called the bar portion of the coronary band. It is also covered with villi, which are directly continous with those of the fleshy frog. The coronary band secretes the principal part (middle layer) of the horny wall of the hoof, including the bar portion (bars) of the wall.

3. The fleshy wall, or podophyllous tissue (Figs. 27, 28, d, and 29, a), is all that portion of the pododerm on which there are fleshy leaves. This leafy tissue covers the anterior surface of the os pedis and the lower portion of the external surface of the lateral cartilages. At the bulbs of the heels it turns inward at a sharp angle and extends forward and inward between the bar portion of the coronary band and the posterior part of the velvety tissue of the sole, nearly to the middle of the solar surface of the foot, to form the laminae of the bars (Fig. 29, a). The fleshy wall and fleshy bars are not covered with villi, but with numerous prominent, parallel, fleshy leaves placed close together, each of which runs in a straight line downward and forward from the coronary band to the lower border of the os pedis. Between the fleshy leaves are deep furrows in which, in a foot which has not been deprived of its horny capsule, lie the horny or insensitive leaves of the wall. The fleshy leaves (podophyllous laminae) are related to one another somewhat as the leaves of a boot; their posterior borders are attached to the body or basement membrane of the fleshy wall, while their anterior borders and sides are free. At their upper ends immediately below the coronary band the leaves are quite narrow, but they gradually increase in width down to the middle, and thereafter maintain that breadth to the lower border of the os pedis, where they terminate in free, fleshy villi, which differ in no respect from those of the fleshy sole. The number and length of the fleshy leaves vary; in a medium-sized foot there are about five hundred, while in a large foot there may be as many as six hundred. On the anterior surface of the os pedis the leaves are thickest and longest; on the sides and quarters they gradually decrease in length, while in the bar region they are the shortest and gradually disappear near the anterior ends of the bars. The width of the leaves decreases as they become shorter. Viewed with the naked eye the leaves appear flat and smooth, but under the microscope one can see on both sides of a fleshy leaf numerous small, fleshy leaflets parallel to one another and extending lengthwise with the larger leaf. The large ones are called principal leaves, and the small ones are known as collateral leaves, or simply as leaflets.

The fleshy leaves (podophyllus tissue) secrete the horny leaves (keraphyllous tissue) and serve to bind the horny wall to the pododerm. The strength of this union is due largely to the dovetailing of the horny leaves and their leaflets with the fleshy leaves and their leaflets.

4. The fleshy sole or velvety tissue of the sole (Fig. 29, b) is that part of the pododerm which covers all the under surface of the foot except the plantar cushion, the bar laminae, and the bar portion of the coronary band. It is sometimes slate-colored or studded with black spots, but is usually dark red. It is thickly set with villi, which are especially long and strong* near its periphery. The fleshy sole covers the solar plexus, or net-work of veins, and secretes the horny scale.

*In order to see the length, thickness, and abundance of the villi of the pododerm, place the foot deprived of its hoof in a clear glass jar and cover it with water, renewing the latter until it is no longer tinged with blood.

5. The velvety tissue of the frog (Fig. 29, c) covers the lower surface of the plantar cushion, and in the region of the bulbs (e) passes insensibly into the perioplic band. In comparison with the fleshy sole, it has much finer and shorter villi and contains fewer blood-vessels. It secretes the soft, horny frog.

(c) The horn capsule or hoof (Fig. 30) is the entire mass made up of the horn-cells secreted from the whole surface of the pododerm, and next to the shoe is the organ with which the horse-shoer has most to do. The horn capsule or hoof is nothing more than a very thick epidermis that protects the horse’s foot, just as a well fitting shoe protects the human foot. The hoof of a sound foot is so firmly united with the underlying pododerm that only an extraordinary force can separate them. In its normal condition the hoof exactly fits the soft structures within it; hence it is evident that local or general contraction of the hoof must produce pressure on the blood-vessels and nerve-endings of the pododerm, disturb the circulation of the blood and the nutrition of the foot, and cause pain.

The hoof is divided into three principal parts, which are solidly united in the healthy foot – namely, the wall, the sole, and the frog. That part of the hoof which is almost wholly invisible when the foot is on the ground (Fig. 30, b, c), and which protects the foot in front and upon the sides, is known as the wall. In position, course, direction, and arrangement of its parts it simulates the different parts of the pododerm from which it is developed. It extends from the edge of the hair just above the coronary band to the ground; backward it gradually decreases in height (length), passes around the bulbs of the heels, and turns forward and inward (Fig. 32, d, e, and 34, a, b) to form the bars, which are finally lost in the edge of the sole near the summit of the frog. It thus forms at each heel an angle (Fig. 31, d, and 32, d) known as a buttress, which encloses a branch of horny sole. Externally the wall is smooth, covered with the varnish-like periople, and presents indistinct ring-like markings (Fig. 30). Its inner surface, on the contrary presents a great number of horn-leaves which are spoken of collectively as the keraphyllous tissue (Figs. 32, g, and 35, f). The upper or coronary border of the wall is thin and flexible, and on its inner aspect is the coronary groove, into which fits the coronary band (Fig. 30, f). The lower border of the wall, called the “bearing-edge” or plantar border (Fig. 31, a), is the one to which the horseshoe is fastened. By dividing a hoof from before to behind along its median line, outer and inner halves or walls are produced, and by dividing the entire lower circumference of the wall into five equal parts or sections, a toe, two side walls or mammae, and two quarters will be exhibited (Figs. 32 and 33). In order to designate these regions of the hoof still more accurately, they are spoken of as outer and inner toes, quarters, and heels.

The direction (slant) and length of the wall vary in one and the same hoof, as well as between fore and hind hoofs. The portion of the wall of fore hoofs is the most slanting – that is, forms the most acute angle with the surface of the ground – and is also the longest. Towards the quarters the wall gradually becomes very nearly vertical; in almost all hoofs the posterior part of the quarters slants downward and inward towards the median vertical antero-posterior plane of the foot. At the same time the wall, in passing back from the toe to the heel, becomes gradually shorter in such a manner in that the heights of the toe, side walls, and quarters are related to one another about as 3:2:1 in front hoofs and as 4:3:2 in hind hoofs. The outer wall is, as a rule, somewhat more slanting than the inner. Viewing a foot in profile, the toe and heel should be parallel; that is, the line from the hair to the ground at the toe should be parallel to the line from the hair to the ground at the buttress. All deviations of the wall from a straight line (outward or inward bendings) are to be regarded as faults or defects.

The thickness of the wall is also variable. In front hoofs the wall is thickest at the toe, and becomes gradually thinner towards the quarters, while in hind hoofs, there is very little difference in the thickness of the wall of the toe, sides, and quarters. The more slanting half of the hoof is always the thicker; thus, for example, the outer wall of a base-wide foot is always longer and more oblique than the inner wall, and is also thicker. According to Mayer, the thickness of the wall at the toe varies from three- to five-eights of an inch, and at the quarters from two to three eighths of an inch. These measurements are dependent upon the size and breeding of the horse.

The horn wall is composed of three superposed layers. These from without to within are: (1) the periople, secreted by the perioplic band. It is very thin, glistening, and varnish-like in appearance, and covers the entire outer surface of the wall except where it has been removed by the rasp, and prevents rapid evaporation of moisture from the horn. (2) The middle or protective layer (Fig. 35, d) is the thickest, strongest, and most important of the three layers; it forms the principle mass of the wall, and is developed or secreted by the coronary band, which fits into the coronary groove. There are in the coronary groove a great number of small, funnel-shaped openings into which project the horn-producing villi or papillae of the coronary band. (3) The inner layer or keraphyllous layer (Fig. 35, f) consists of prominent, parallel horn-leaves lying side by side over the entire inner surface of the middle layer of the wall, and continuing beyond the buttresses to the ends of the bars (Fig. 35, f’). This layer of horn-leaves (keraphyllous layer) has in a general way about the same shape and arrangement as the layer of fleshy leaves (podophyllous layer) which secretes it; for the horn-leaves fit in with the fleshy leaves in such a way that every fleshy leaf is embraced by two horn-leaves, and every horn-leaf by two fleshy leaves (Fig. 36). The keraphyllous layer and the horn of the inmost part of the middle or protective layer are always white, even in pigmented (colored) hoofs.

The horn sole (Fig. 31, f, and Fig. 35, g) is secreted by the velvety tissue of the sole. A sole from which the loose flakes of old horn have been removed is about as thick as the wall. It covers the under surface of the foot, and presents upon its upper surface a convexity which exactly fits into the concavity on the under surface of the os pedis. This upper surface is thickly covered by a multitude of minute funnel-shaped openings for the reception of the villi of the velvety tissue of the sole (Fig. 37). The lower surface of the sole is more or less concave, rough, uneven, and often covered by loose scales of a dead horn. Behind, the sole presents a triangular opening whose borders lie partly in contact with the horny frog and partly with the bars. This opening or re-entering angle divides the sole into a body (Fig. 31, f) and two wings or branches (Fig. 31, f’) The outer border of the sole unites through the medium of the white line with the lower part of the inner surface of the wall – that is, with the keraphyllous layer of the wall. This white line (Figs. 31, g, and 35, h), of so much importance to the horse-shoer, is formed by the horn leaves, and by those short plugs of tubular horn which are secreted by the villi that are always found at the lower ends of the fleshy leaves. The white line may be said to exist wherever the horn-leaves can be discerned upon the plantar surface of the hoof. It not only passes around the conference of the sole from heel to heel, but may be followed forward from the buttresses along the bars almost to the summit of the frog. The horn of the white line is soft, unpigmented (white), and possesses so very little resistance (strength) that it is often found crumbling or even absent in places. The visible part of the white line is usually of a grayish-black color, owing to the working in from below of dirt and liquid manure, and to staining by rust from the nails. The white line is very important, since it serves as the point from which we judge of the thickness of the wall, and because the horseshoe nail should penetrate it.

The frog (Figs. 31, h, 35, k, l, 38, and 39), secreted by the velvety tissue covering the plantar cushion and presenting almost the same form as the latter, lies as a wedge between the bars and between the edges of the sole just in front of the bars, with both of which structures it is intimately united. Its horn is quite soft and very elastic. The median lacuna or cleft of the frog (Fig. 31, l) divides it into two branches (Fig. 31, i), which pass backward and outward into the horny bulbs (Fig. 31, k). In front of the median lacuna the two branches unite to form the body of the frog (Fig. 31, h), which ends in a point, designated the point, apex, or summit of the frog. On the upper surface of the frog, directly over the median cleft of the lower surface, there is a small projection called the frog-stay (Figs. 35, l, 38 and 39, b), which fits into the median cleft of the plantar cushion. Besides, the upper surface of the frog shows many minute openings, similar to but smaller than those of the sole and coronary groove, for the reception of villi. In unshod hoofs the frog, sole, bars, and bearing-edge of the wall are on a level; that is, the plantar surface of such hoofs is perfectly flat.

The minute structure of the horn can scarcely be considered in detail in an elementary treatise such as this is. However, a few of the most important facts are as follows:

If we carefully examine the transverse section of the horn of the wall (Fig. 41), sole, or frog, we will see with the naked eye, though much better with a magnifying glass, many minute points quite close to one another, and greatly resembling the small openings which we have seen in the coronary groove of the wall and on the upper surface of the horny sole and frog. If, now, we examine a longitudinal section of the wall (Fig. 40) or sole, we will see a number of fine, dark stripes which are straight, parallel, quite close to one another, of different widths, are which are separated by bands of lighter horn also of different widths. A thin section or slice of the wall taken at right angles to the direction of these dark lines (Figs. 41) shows us that the minute points that are visible to the naked eye, when held up to the light or moderately magnified, prove to be small openings (Fig. 41, a). Since these openings, shown in Fig. 41, represent the dark lines shown in Fig. 40, because an opening is found wherever there is a dark line, we must regard all dark lines seen in longitudinal sections of wall, sole and frog as hollow cylinders or tubes, though they are not always hollow, but are often filled with loosely adjusted, crumbling, broken-down horn-cells. The dark edges of the openings (a) consist of thick layers of horn-cells (tube-walls). The entire structure is called a horn-tube, and the lighter-colored masses of horn (Fig. 41, b) between the tubes are known as intertubular horn.

With the exception of the horny leaves of the wall and bars, all the horn of the hoof is composed of horn-tubes and intertubular horn.

The horn-tubes of the wall, sole, and frog always run downward and forward parallel to the direction of the wall at the toe – that is, in a direction parallel with the inclination of the hoof as a whole. Although the wall, sole, and frog differ from one another considerably with respect to the size and number of the horn-tubes, the quality of the intertubular horn, and the thickness and strength of the horn-cells, these differences are only of subordinate interest or importance to the horse-shoer; but he who desires to learn more of this matter is referred to the work of Leisering & Hartmann, “Der Fuss des Pferdes in Rücksicht auf Bau, Verrichtungen und Hufbeschlag,” eighth edition, Dresden, 1893. This book also treats of the variations in the quality of hoofs, which is very important for the practical horse-shoer to know. It, furthermore, considers the solidity and strength of the horn of the different parts of the hoof.

With the respect to solidity, two kinds of horn are distinguished – namely, hard and soft horn. The periople, the white line, and the frog are soft horn structures; the middle layer of the wall and the sole are hard or solid horn. The wall, however, is somewhat harder and more tenacious than the sole, for the latter passes off in more or less large flakes (exfoliates) or crumbles away on its lower surface, at least in shod feet, while no such spontaneous shortening occurs in the wall.

Soft horn differs from hard horn in that its horn-cells never become hard and horn-like. It is very elastic, absorbs water quickly, and as readily dries out and becomes very hard and brittle and easily fissured and chapped. With respect to quality we distinguish good and bad horn; the former is fine and tenacious (tough), the latter coarse and either soft and crumbling or hard and brittle. If not dried out, all horn is elastic, though soft horn is more elastic than hard. All horn is a poor conductor of heat.

The relative positions of the various parts of the foot are shown in Fig. 42.

Fig. 43 represents the exterior of a well-formed foot.